Analysis of the Near Ultraviolet Electronic Transition of Benzene

The absorption spectrum of benzene at 2800–2200A has been analyzed. The vibrational structure of the system has been found to be in agreement with the selection rules for a forbidden transition (1A1g→1B2u). The transition becomes possible when vibrations of type Eg+ distort the molecule. Only carbon frequencies have been found to be effective. The interpreted data are collected in series on page 211. The analysis is corroborated by comparison with the absorption of solid benzene at —259°C, with the absorption spectrum of heavy benzene and with the fluorescence spectra of both benzenes.